You can't add different loader without accessing private APIs, but you can add background image:
UIImageView *rcImageView =
[[UIImageView alloc] initWithImage:
[UIImage imageNamed: @"refreshControl.png"]];
[self.refreshControl insertSubview:rcImageView atIndex:0];
assuming self is an instance of UITableViewController subclass.
Image size you need is 320x43px (@2x 640x86px), the middle area (approximately 35px) will be covered by the loader animation.
I show application logo there...
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